Emission control is one of the important technologies installed in modern motor vehicles. Emission control systems are designed to implement such emission control. Specifically, these emission control systems are commonly used for minimizing these particular components contained in the exhaust emissions from the internal combustion engine (engine) as by-products of combustion leaving the engine.
An absorbent for absorbing hydrocarbons (HC) as one of the main particular components in the exhaust emissions is normally used in the emission control system. Specifically, this absorbent is characterized to absorb the HC with its temperature lower than a desorbing temperature T1, and desorb the absorbed HC with its temperature equal to or higher than the desorbing temperature T1. An oxidation catalyst for oxidizing HC is also normally used in the emission control system. Specifically, this oxidation catalyst is characterized to activate with its temperature equal to or higher than an activation temperature T2. In the activated state, the oxidation catalyst enables the HC desorbed from the absorbent to be oxidized. Note that the activation temperature T2 is usually set to be higher than the desorbing temperature T1.
Japanese Patent Application Publications No. 2004-116370 and 2001-164930 disclose, at cold start of the engine, control for retarding engine ignition timing to raise the temperature of the oxidation catalyst up to the activation temperature T2 early after the start-up of the engine. This control to raise the temperature of the catalyst including the ignition-timing retard control will also be referred to as “catalyst warm-up control”.
If the catalyst warm-up control were executed immediately after start-up of the engine, the temperature of the absorbent for the HC would be equal to or higher than the desorbing temperature T1 with the amount of the absorbed HC being not up to a given saturated amount thereof. This could not make full use of the absorption capabilities of the absorbent.
In order to address this problem, an emission control system disclosed in the Patent Publication No. 2004-116370 is configured to start the catalyst warm-up control at the time when the absorption temperature reaches the desorbing temperature T1.